1. Field of the Invention
This invention relates to gear forming. More particularly, it pertains to cold-rolling of gear teeth in a virgin, i.e., substantially smooth, surface of a relatively large diameter gear blank by a forming roll in which all teeth are identical and are conjugate to the teeth to be found in the blank.
2. Review of the Prior Art
Commonly owned U.S. Pat. No. 3,877,273 describes method and apparatus for forming, solely by a cold-rolling operation, fully-finished gear teeth in a virgin surface of a gear blank. A virgin surface, in the context of both the prior patent and the present invention, means the surface of the blank into which gear teeth are to be formed and which, prior to the beginning of the cold-rolling operation, does not define either rudimentary gear teeth (as compared with gear cold-rolling processes alternative to gear shaving, for example) or depressions or other features indicative of the spacing between adjacent ones of the teeth to be formed. U.S. Pat. No. 3,877,273 describes such cold-rolling of gears both in terms of gears sufficiently small that they are formed in a centerless rolling machine and in terms of relatively larger gears having sufficient intrinsic structural strength to permit the gear rolling operation to occur in a lathe or chucking machine. This invention pertains to gears of the latter class, i.e., gears formed in blanks of sufficient strength as not to require use of centerless cold-rolling techniques.
The large gear cold-rolling apparatus and procedures described in U.S. Pat. No. 3,877,273 with reference to FIGS. 1-3 thereof are fully effective. The use of these apparatus and procedures, however, requires that the blank, into which gear teeth are to be cold-rolled, be very precisely fabricated. The diameter of the blank must be defined with great precision; a gear blank only slightly oversize or undersize will result in the generation of either too many or too few teeth or in the generation of significantly inaccurate teeth. Precision machining operations are costly, both in terms of the time required for their proper performance, in terms of the prevailing wages paid to persons of the requisite levels of skill, and in terms of the machines needed to perform such operations. A principal advantage of cold-rolling gear forming procedures is that they are not labor intensive and are comparatively fast, and thus are less costly than other gear forming techniques. The need for precision fabrication of gear blanks offsets the beneficial economic advantage of the gear rolling procedures described in the prior patent.
A need exists for a cold-rolling gear forming apparatus and procedure which is useful with relatively large diameter gear blanks and which is not dependent on the gear blanks being fabricated to high levels of precision, especially as to diameter.